The solvent-producing clostridia are well known for their ability to produce acetone, butanol and isopropanol in industrial fermentation. Production of these compounds occurs in cells that have completed a metabolic switch under specific growth conditions. Knowledge of the regulation of the metabolic switch will make the industrial process more reliable. From an isopropanol-producing strain Clostridium beijerinckii NRRL B593, a gene which encodes a putative NtrC-like regulatory protein was cloned and sequenced. The gene codes for a polypeptide of 632 amino acids and has been designated the stc gene. Expression of the stc gene was confirmed by RT-PCR. The co-presence of the stc gene with the adh gene which encodes a primary/secondary alcohol dehydrogenase in isopropanol-producing clostridia suggests that the stc gene may be functionally related to isopropanol production.

From C. beijerinckii NRRL B592, a region which encompassed the solvent-production genes ald (aldehyde dehydrogenase), ctfA and ctfB (acetoacetate: butyrate/acetate CoA-transferase) and part of adc (acetoacetate decarboxylase) was cloned and sequenced. The organization of these genes was similar to that in C. beijerinckii NRRL B593. Northern analysis indicated that these four genes were co-transcribed on the same messenger RNA in C. beijerinckii NRRL B593. Therefore, in C. beijerinckii, the sol operon consists of the ald -ctfA-ctfB-adc genes, which differs from the sol operon in Clostridium acetobutylicum.